7. Project Summary/Abstract Arsenic is a contaminant found in drinking water and food stuffs, resulting in the exposure of millions of people to concentrations above the current US EPA and WHO drinking water standard. Despite its prevalence, the mechanisms by which it impacts development are still not well understood. Evidence from epidemiological and rodent studies indicates that embryonic and fetal exposure to arsenic is associated with altered muscle function, reduced weight gain, and neurobehavioral effects such as reduced IQ, impaired spatial memory, and changes in behavior. We have using mouse embryonic stem (ES) cells to examine changes in differentiation following a short-term arsenic exposure, and found that arsenic inhibits their differentiation into skeletal myotubes and neurons by reducing the expression of lineage-specific transcription factors, including MyoD, myogenin, NeuroD, and neurogenin. Our lab has recently created a series of ES cell lines that have been chronically exposed to 0.1?M or 7.5pppb arsenic, a concentration below the drinking water standard. Our preliminary data shows that cells ES exposed to arsenic for >16 weeks have lost their ability to differentiate into adult cell types. Thus, the goal of this application in to assess the time course, the persistence of the phenotype, the mechanisms behind this loss of differentiation ability, and whether a similar loss of differentiation happens to neural stem cell in vivo. In the first and second aims, we determine the time course of this phenotype, assess whether the loss of differentiation persists following a recovery period, and assess the mechanisms responsible for aberrant differentiation, including changes in apoptosis, proliferation, apoptosis, and epigenetic modifications. In the third aim, we will ascertain whether neuronal stem cell proliferation, migration, and differentiation is also impacted during an in vivo embryonic arsenic exposure by investigating whether certain cell types are more sensitive to particular exposure time points. These studies will further our understanding by which arsenic exposure during development causes impaired repair after an injury, reduced memory development, sensory impairment, and motor changes. More importantly, our research will determine whether exposed populations can ever ?recover? from a prenatal arsenic exposure